Discovery of molecular sieves containing octahedral framework chains represents an important new branch of molecular sieve science. Reference is made to U.S. Pat. No. 4,853,202 and U.S. Pat. No. 4,938,939 (Kuznicki et al).
ETS-4 described in U.S. Pat. No. 4,938,939, the entire disclosure of which is herein incorporated by reference, is a small-pored titano-silicate molecular sieve containing such chains. ETS-4 is characterized by relatively poor thermal stability in the predominantly sodium exchange form in which it is typically synthesized, generally losing substantial structure and porosity near its dehydration temperature of approximately 200.degree. C. However, it is reported in U.S. Pat. No. 4,938,939, that
"Members of the family of molecular sieves designated ETS-4 in the rare earth-exchanged form have a high degree of thermal stability of at least 450.degree. C. or higher depending on cationic form, . . . . "
The thermal instability of the as-synthesized forms of ETS-4, usually mixed sodium and potassium forms, or of the sodium form of ETS-4 is disclosed in Kuznicki et al, Synthesis and Absorbent Properties of Titanium Molecular Sieves, appearing in Molecular Sieves, Edited by Occelli et al, Van Nostrum Reinhold, New York, 1992, pgs. 427-443, Philippou, A., Anderson, M. W. Zeolites, Vol. 16, 1996. pgs. 98-107. and Naderi. M., Anderson, M. W. Zeolites. Vol. 17. 1996, pgs. 437-443.
Water must generally be removed from a molecular sieve zeolite before it can be effectively employed as a sorbent. It is obvious that a dehydrated sieve will have limited utility as a sorbent unless it is stable at and beyond the temperature at which it is dehydrated.
It has been reported that a phase transformation in ETS-4 occurs at 500-700.degree. C. This change is attributed to the formation of narsarsukite. The regime between drying at approximately 200.degree. C. and narsarsukite formation at higher temperatures has been reported to be essentially XRD amorphous for the sodium form of ETS-4. Reference is made to Naderi. M. and Anderson, M. W. Zeolites, Vol. 17, 1996, pgs. 437-443.
In the process of this invention, systematic pore size reduction results in an entirely new zeolite and progresses smoothly and may be frozen at a desired point by cooling the material and quenching the process. This new zeolite retains substantial porosity as measured by its ability to sorb water and other molecules.